[ricardobeat]

The main difference is that the JS source is being parsed, and most of the build steps operate on the AST. This is what allows things like transpiling modern language features to more broadly supported versions, doing dependency resolution, pruning, and automatic splitting (imagine your Makefile with 300 js files). Remember that JS does not yet have a built-in module system - simply pasting source files together means you'll be rolling your own.

[RonanTheGrey]

Yep, alot of people forget that - because JS is delivered to the browser and not preemptively downloaded (or executed in a compiled form on a server), there's NO opportunity to do things like optimization, tree shaking, etc. that other JITs do, or compiled languages do.

And the moment you accept that it is necessary (and why wouldn't it be - languages are for developers, not computers, and that means they by necessity will include cruft), you require a build system to at the very least, run the optimizer and minimizer.

It seems like a trivial problem but it isn't. We are long past the days when JS was only used to make an image blink.